Marissa

Marissa Cooper (played by Mischa Barton) – (Seasons 1 – 3): The first of the "core four" to leave the series at the end of season three. Marissa is arguably the most conflicted of the main characters, frequently battling with drugs and alcohol. Marissa's relationships with her parents, boyfriends, and fellow classmates are often tumultuous. She is Summer's best friend and Ryan's on and off love interest. Marissa engages in various romances throughout the series (in addition to her relationship with Ryan), notably with her family's gardener D.J., Seth's ex-girlfriend Alex, and high school drop-out Kevin Volchok. In the third season finale, Marissa decides to work with her father on his yacht, however, on the way to the airport with Ryan, Volchok runs them off of the road, leading to her death. Marissa's death plays a large role throughout season 4 as the other characters grieve.